Mixing and phase separation in molecular fluid mixtures

The equation of state for a hard convex body (HCB) fluid mixture, which is based on the scaled particle theory, is utilized to derive the Helmholtz free energy, F, and the concentration fluctuations, S.,(O), to investigate the thermodynamic stability of athermal and not athermal molecular fluid mixtures. The role of the size and the non-sphericity geometrical factor of the molecule on the stability of the mixture is critically examined. The energetics of long-range attractive forces for not athermal mixtures have been introduced through the double Yukawa potential in conjunction with a realistic distribution function. The formalism allows one to investigate the properties of molecular mixtures under induced conditions of extreme temperature and pressure. The results suggest that geometrical factors coupled with energetics play a dominant role in phase separation.